[libcxx] r323171 - [cmake] Always respect existing CMAKE_REQUIRED_FLAGS when adding additional ones.

[Don Hinton via cfe-commits]

Author: dhinton
Date: Mon Jan 22 19:30:23 2018
New Revision: 323171

URL: http://llvm.org/viewvc/llvm-project?rev=323171&view=rev
Log:
[cmake] Always respect existing CMAKE_REQUIRED_FLAGS when adding additional ones.

* Previously part of https://reviews.llvm.org/D41622.

Modified:
    libcxx/trunk/cmake/Modules/CheckLibcxxAtomic.cmake

Modified: libcxx/trunk/cmake/Modules/CheckLibcxxAtomic.cmake
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/cmake/Modules/CheckLibcxxAtomic.cmake?rev=323171&r1=323170&r2=323171&view=diff
==============================================================================
--- libcxx/trunk/cmake/Modules/CheckLibcxxAtomic.cmake (original)
+++ libcxx/trunk/cmake/Modules/CheckLibcxxAtomic.cmake Mon Jan 22 19:30:23 2018
@@ -9,7 +9,7 @@ INCLUDE(CheckCXXSourceCompiles)
 
 function(check_cxx_atomics varname)
   set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
-  set(CMAKE_REQUIRED_FLAGS "-nodefaultlibs -std=c++11 -nostdinc++ -isystem ${LIBCXX_SOURCE_DIR}/include")
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nodefaultlibs -std=c++11 -nostdinc++ -isystem ${LIBCXX_SOURCE_DIR}/include")
   if (${LIBCXX_GCC_TOOLCHAIN})
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} --gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}")
   endif()